grub-mkconfig/10_linux: Support multiple early initrd images

Add support for multiple, shared, early initrd images. These early
images will be loaded in the order declared, and all will be loaded
before the initrd image.

While many classes of data can be provided by early images, the
immediate use case would be for distributions to provide CPU
microcode to mitigate the Meltdown and Spectre vulnerabilities.

There are two environment variables provided for declaring the early
images.

* GRUB_EARLY_INITRD_LINUX_STOCK is for the distribution declare
  images that are provided by the distribution or installed packages.
  If undeclared, this will default to a set of common microcode image
  names.

* GRUB_EARLY_INITRD_LINUX_CUSTOM is for user created images. User
  images will be loaded after the stock images.

These separate configurations allow the distribution and user to
declare different image sets without clobbering each other.

This also makes a minor update to ensure that UUID partition labels
stay disabled when no initrd image is found, even if early images are
present.

This is a continuation of a previous patch published by Christian
Hesse in 2016:
http://lists.gnu.org/archive/html/grub-devel/2016-02/msg00025.html

Down stream Gentoo bug:
https://bugs.gentoo.org/645088

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Signed-off-by: Matthew S. Turnbull <sparky@bluefang-logic.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

docs/grub.texi

@@ -1398,6 +1398,25 @@ for all respectively normal entries.
 The values of these options replace the values of @samp{GRUB_CMDLINE_LINUX}
 and @samp{GRUB_CMDLINE_LINUX_DEFAULT} for Linux and Xen menu entries.
 
+@item GRUB_EARLY_INITRD_LINUX_CUSTOM
+@itemx GRUB_EARLY_INITRD_LINUX_STOCK
+List of space-separated early initrd images to be loaded from @samp{/boot}.
+This is for loading things like CPU microcode, firmware, ACPI tables, crypto
+keys, and so on. These early images will be loaded in the order declared,
+and all will be loaded before the actual functional initrd image.
+
+@samp{GRUB_EARLY_INITRD_LINUX_STOCK} is for your distribution to declare
+images that are provided by the distribution. It should not be modified
+without understanding the consequences. They will be loaded first.
+
+@samp{GRUB_EARLY_INITRD_LINUX_CUSTOM} is for your custom created images.
+
+The default stock images are as follows, though they may be overridden by
+your distribution:
+@example
+intel-uc.img intel-ucode.img amd-uc.img amd-ucode.img early_ucode.cpio microcode.cpio
+@end example
+
 @item GRUB_DISABLE_LINUX_UUID
 Normally, @command{grub-mkconfig} will generate menu entries that use
 universally-unique identifiers (UUIDs) to identify the root filesystem to

util/grub-mkconfig.in

@@ -147,6 +147,12 @@ if [ x"$GRUB_FS" = xunknown ]; then
     GRUB_FS="$(stat -f --printf=%T / || echo unknown)"
 fi
 
+# Provide a default set of stock linux early initrd images.
+# Define here so the list can be modified in the sourced config file.
+if [ "x${GRUB_EARLY_INITRD_LINUX_STOCK}" = "x" ]; then
+	GRUB_EARLY_INITRD_LINUX_STOCK="intel-uc.img intel-ucode.img amd-uc.img amd-ucode.img early_ucode.cpio microcode.cpio"
+fi
+
 if test -f ${sysconfdir}/default/grub ; then
   . ${sysconfdir}/default/grub
 fi
@@ -211,6 +217,8 @@ export GRUB_DEFAULT \
   GRUB_CMDLINE_NETBSD \
   GRUB_CMDLINE_NETBSD_DEFAULT \
   GRUB_CMDLINE_GNUMACH \
+  GRUB_EARLY_INITRD_LINUX_CUSTOM \
+  GRUB_EARLY_INITRD_LINUX_STOCK \
   GRUB_TERMINAL_INPUT \
   GRUB_TERMINAL_OUTPUT \
   GRUB_SERIAL_COMMAND \

util/grub.d/10_linux.in

@@ -136,9 +136,13 @@ EOF
   if test -n "${initrd}" ; then
     # TRANSLATORS: ramdisk isn't identifier. Should be translated.
     message="$(gettext_printf "Loading initial ramdisk ...")"
+    initrd_path=
+    for i in ${initrd}; do
+      initrd_path="${initrd_path} ${rel_dirname}/${i}"
+    done
     sed "s/^/$submenu_indentation/" << EOF
 	echo	'$(echo "$message" | grub_quote)'
-	initrd	${rel_dirname}/${initrd}
+	initrd	$(echo $initrd_path)
 EOF
   fi
   sed "s/^/$submenu_indentation/" << EOF
@@ -188,7 +192,15 @@ while [ "x$list" != "x" ] ; do
   alt_version=`echo $version | sed -e "s,\.old$,,g"`
   linux_root_device_thisversion="${LINUX_ROOT_DEVICE}"
 
-  initrd=
+  initrd_early=
+  for i in ${GRUB_EARLY_INITRD_LINUX_STOCK} \
+	   ${GRUB_EARLY_INITRD_LINUX_CUSTOM}; do
+    if test -e "${dirname}/${i}" ; then
+      initrd_early="${initrd_early} ${i}"
+    fi
+  done
+
+  initrd_real=
   for i in "initrd.img-${version}" "initrd-${version}.img" "initrd-${version}.gz" \
 	   "initrd-${version}" "initramfs-${version}.img" \
 	   "initrd.img-${alt_version}" "initrd-${alt_version}.img" \
@@ -198,11 +210,22 @@ while [ "x$list" != "x" ] ; do
 	   "initramfs-genkernel-${GENKERNEL_ARCH}-${version}" \
 	   "initramfs-genkernel-${GENKERNEL_ARCH}-${alt_version}"; do
     if test -e "${dirname}/${i}" ; then
-      initrd="$i"
+      initrd_real="${i}"
       break
     fi
   done
 
+  initrd=
+  if test -n "${initrd_early}" || test -n "${initrd_real}"; then
+    initrd="${initrd_early} ${initrd_real}"
+
+    initrd_display=
+    for i in ${initrd}; do
+      initrd_display="${initrd_display} ${dirname}/${i}"
+    done
+    gettext_printf "Found initrd image: %s\n" "$(echo $initrd_display)" >&2
+  fi
+
   config=
   for i in "${dirname}/config-${version}" "${dirname}/config-${alt_version}" "/etc/kernels/kernel-config-${version}" ; do
     if test -e "${i}" ; then
@@ -216,9 +239,7 @@ while [ "x$list" != "x" ] ; do
       initramfs=`grep CONFIG_INITRAMFS_SOURCE= "${config}" | cut -f2 -d= | tr -d \"`
   fi
 
-  if test -n "${initrd}" ; then
-    gettext_printf "Found initrd image: %s\n" "${dirname}/${initrd}" >&2
-  elif test -z "${initramfs}" ; then
+  if test -z "${initramfs}" && test -z "${initrd_real}" ; then
     # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs.  Since there's
     # no initrd or builtin initramfs, it can't work here.
     linux_root_device_thisversion=${GRUB_DEVICE}